Electric vehicle with switched reluctance motor power plant

ABSTRACT

A reluctance machine includes a stator and a rotor. The stator and rotor have a same number of poles. The rotor is configured to rotate about an axis of rotation. Each stator pole is formed of a primary stator pole and an auxiliary stator pole. The auxiliary stator pole is axially aligned with the primary stator pole in the direction of the axis of rotation. Each rotor pole has a length extending in the direction of the axis of rotation sufficient to at least partially cover the primary stator pole and axially aligned auxiliary stator pole. The primary stator poles are actuated with an alternating magnetic field orientation, and the auxiliary stator poles are also actuated with an alternating magnetic field orientation. The field orientations for the primary and auxiliary stator poles are, however, opposite each other such that a primary stator pole its axially aligned auxiliary stator pole have opposite magnetic field orientations.

BACKGROUND

1. Technical Field

The present invention relates generally to electric vehicles and, inparticular, to an electric vehicle using a switched reluctance motor asa power plant.

2. Description of Related Art

With the increase in gasoline prices, and concerns over global warming,there is a significant interest in electric vehicles. While a number ofdifferent types of electric motors have been considered for use inelectric vehicle applications, consideration has recently turned to thepotential use of switched reluctance motors as the power plant for anelectric vehicle.

Reluctance motors are well known in the art. These machines operate onthe tendency of the machine's rotor to move to a position where thereluctance with respect to the stator is minimized (in other words,where the inductance is maximized). This position of minimizedreluctance occurs where the rotor pole is aligned with an energizedstator pole. When operated as a motor, energizing the stator polegenerates a magnetic field attracting the rotor pole towards the statorpole. This magnetic attraction produces a torque causing the rotor torotate and move towards the minimized reluctance position.

Both single-phase and multi-phase switched reluctance motors have beenconsidered for electric vehicle applications. The present disclosurefocuses on single-phase machines.

Reference is now made to FIGS. 1A and 1B which illustrate the generalconfiguration and operation of a simple single phase switched reluctancemotor of the 6/6 topology. The reference to “6/6” indicates that themachine has six rotor poles and six stator poles. The reference to“single-phase” indicates that there is only one stator energizing phase,and thus each of the six poles on the stator are energizedsimultaneously.

The stator 10 includes six poles 12. The rotor 18 is mounted to a shaft20, and the shaft is supported by a housing and bearings (not shown)that allow for rotational movement of the rotor relative to the stator10. The rotor 18 also includes six poles 22. The stator poles 12 androtor poles 22 are salient poles, as is known in the art.

Each stator pole 12 is wound with a winding 14. The windings 14 for thesix stator poles 12 are electrically connected in parallel and currentis supplied thereto from a switched power supply 16. The windingdirection for each stator pole winding 14 is indicated using an “×” and“●” nomenclature, where “×” indicates movement of charge into the page,and “●” indicates movement of charge out of the page. So, it will benoted with the windings 14 oriented as illustrated in FIGS. 1A and 1B,the magnetic field orientation of the stator poles when actuatedalternates /N-S-N-S-N-S/ with respect to each stator pole around thecircumference of the stator 10.

The magnetic flux paths 17 are shown with respect to the actuated statorpoles 12. These paths flow from a first stator pole, cross the air gapto a first rotor pole, and flow from the first rotor pole through theweb of the rotor to a second rotor pole adjacent the first rotor pole,cross the air gap to a second stator pole adjacent to the first statorpole, and flow from the second stator pole back to the first statorpole.

FIG. 1A shows the approximate angular orientation of the rotor 18 when aswitched power supply 16 that is coupled to the windings 14 of thestator 12 poles may be actuated. Current is supplied to the stator polewindings 14 so as to simultaneously energize the six poles 12 of thestator 10. The six rotor poles 22 are attracted to the energized statorpoles 12, producing a torque 24 on the shaft 20 and causing the rotor torotate. The rotor poles 22 move towards the energized stator poles 12 inan effort to minimize the reluctance.

As the rotor poles 22 move towards the position of minimized reluctance(i.e., when the rotor pole 22 is aligned with the stator pole 12) asshown in FIG. 1B, the switched power supply 16 is de-actuated. Angularmomentum is preserved and the rotor continues to rotate such that therotor pole 22 passes by the de-energized stator pole 12. After a delayperiod which allows the rotor pole 22 to move sufficiently away from thestator pole 12 (i.e., move closer to the next stator pole), the switchedpower supply 16 is actuated again (see, FIG. 1A), and the processrepeats.

It will be noted that proper operation of the motor is dependent on thetiming of switched power supply 16 actuation and thus the actuation ofthe stator poles. That timing of actuation is driven by the angularposition of the rotor poles relative to the stator poles. Thus, themotor further includes an angular position sensor 26 coupled to theshaft 20 to detect the angular position of the rotor poles relative tothe stator poles. The angular position information output from theangular position sensor 26 is supplied to the switched power supply 16to assist in controlling the timing of switched power supply 16actuation of the stator poles 12.

Single-phase motors are believed to have limited use as an electricvehicle power plant because of concerns with, among other issues,start-up, limited maximum output torque, variations in output torque(known as torque ripple), energy and heat dissipation, and noise.However, single-phase motors advantageously need a relatively moresimple control system than is used in multi-phase reluctance motors, andare preferred over multi-phase motors in many applications for thisreason. There is accordingly a need in the art for an improvedsingle-phase switched reluctance motor which addresses the limitationsand concerns of prior art single-phase configurations while maintainingthe advantages of simple control. There is further a need for asingle-phase configuration which can support sufficient torque output inan electric vehicle application.

SUMMARY

In an embodiment, an electric vehicle comprises at least two drivewheels and a power plant for supplying torque for causing rotation ofthe at least two drive wheels. The power plant comprises a switchedreluctance motor. The switched reluctance motor comprises a statorhaving a plurality of stator poles and a rotor having a plurality ofrotor poles. The rotor is configured to rotate about an axis ofrotation. Each of the stator poles comprises: a primary stator pole andan auxiliary stator pole. The auxiliary stator pole is axially alignedwith the primary stator pole in the direction of the axis of rotation.Each rotor pole has a length extending in the direction of the axis ofrotation sufficient to at least partially cover the primary stator poleand axially aligned auxiliary stator pole.

In an embodiment, the vehicle comprises at least four drive wheels andthe switched reluctance motor power plant supplies torque for causingrotation of the at least four drive wheels.

In an embodiment, the vehicle further comprises a transmission coupledbetween the switched reluctance motor power plant and the at least twodrive wheels.

In an embodiment, the power plant comprises a first power plantsupplying first torque for actuating a first one of the at least twodrive wheels and a second power plant supplying second torque foractuating a second one of the at least two drive wheels, each one of thefirst and second power plants comprising a switched reluctance motor.

In an embodiment, the vehicle further comprises a battery bank forsupplying electric power to the reluctance motor.

In an embodiment, the primary stator pole and auxiliary stator pole haveseparate windings.

In an embodiment, the windings for the primary stator poles areelectrically connected in parallel.

In an embodiment, the pairs of the windings for the auxiliary statorpoles are electrically connected in parallel.

In an embodiment, the separate windings for the primary stator poles andauxiliary stator poles are electrically connected in parallel. Currentflow in the windings for the auxiliary stator poles, however, isrestricted to a direction opposite current flow in the windings for theprimary stator poles.

In an embodiment, a switching transistor is coupled in series with thewindings for the primary stator poles and the windings for the auxiliarystator poles.

In an embodiment, actuation of the transistor causes current flow in thewindings for the primary stator poles during a first phase of statoractuation, while deactivation of the transistor causes current flow inthe windings of the auxiliary stator poles during a second phase ofstator actuation.

In an embodiment, the primary stator poles are simultaneously actuatedand produce magnetic fields with alternating magnetic fieldorientations. In an embodiment, the auxiliary stator poles aresimultaneously actuated and produce magnetic fields with alternatingmagnetic field orientations. In an embodiment, the alternating magneticfield orientations for the primary stator poles are opposite thealternating magnetic field orientations for the auxiliary stator poles.

In an embodiment, when a primary stator pole and axially alignedauxiliary stator pole are actuated, each produces a magnetic field andthe produced magnetic fields have opposite orientations.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the method and apparatus of the presentinvention may be acquired by reference to the following DetailedDescription when taken in conjunction with the accompanying Drawingswherein:

FIGS. 1A and 1B (previously discussed) illustrate the generalconfiguration and operation of a simple single phase switched reluctancemachine of the 6/6 topology;

FIG. 2 illustrates the general configuration of a single phase switchedreluctance machine of the N/N* topology;

FIG. 3 illustrates a cross-sectional view taken along lines 3-3 of FIG.2;

FIG. 4 illustrates a spacer ring member for use in making a laminatedstator;

FIG. 5 illustrates a stator pole ring member for use in making alaminated stator;

FIG. 6A illustrates the winding of the primary stator poles;

FIG. 6B illustrates the winding of the auxiliary stator poles;

FIG. 7A illustrates the parallel circuit connection of the windings forthe primary stator poles of FIG. 6A;

FIG. 7B illustrates the serial/parallel circuit connection of thewindings for the auxiliary stator poles of FIG. 6B;

FIG. 8 illustrates a schematic diagram of a drive circuit for theswitched reluctance machine;

FIGS. 9A-9D illustrate operation of the motor;

FIG. 9E illustrates magnetic flux paths with respect to the rotor andstator poles;

FIG. 10 illustrates a partial cross-section and side view of anassembled switched reluctance machine;

FIGS. 11A and 11B illustrate a partial cross-section and side view foralternative arrangements of an assembled stacked multiple switchedreluctance machine;

FIG. 11C illustrates angular offsetting of the stator poles for anassembled stacked multiple switched reluctance machine as shown in FIG.11A;

FIG. 12 illustrates a schematic diagram of a drive circuit for theswitched reluctance machine of FIGS. 11 a and 11B;

FIG. 13 illustrates a schematic diagram of an angular position sensorand drive control circuit used in FIGS. 8 and 12;

FIG. 14 illustrates a heat dissipation configuration; and

FIGS. 15 and 16 illustrate use of the switched reluctance machine asdescribed herein as the power plant for an electric vehicle application.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is now made to FIG. 2 wherein there is shown a schematic endview of a first embodiment of a single-phase switched reluctancemachine. The single phase switched reluctance machine is generally ofthe N/N* topology, in this exemplary implementation N=6, but it will beunderstood that N could be any even integer (preferably N being greaterthan or equal to six, although N=2 or N=4 may be suitable in small orlight duty applications). The reference to “N/N*” indicates that themachine has N rotor poles and N* stator poles, wherein the “*”designation indicates that each of the N stator poles comprises thecombination of a primary stator pole PSP and an axially alignedauxiliary stator pole ASP (the axial alignment being in the direction ofthe axis of rotor rotation). The reference to “single-phase” indicatesthat there is only one overall switched stator energizing phase. Thespecific energization process for the primary stator poles PSP andauxiliary stator poles ASP will be described in more detail below.

The stator 110 of the switched reluctance machine is illustrated in anexemplary manner to include N=6 six stator poles 112. The rotor 118 ismounted to a shaft 120, and the shaft is supported for rotationalmovement relative to the stator 110. The rotor 118 is formed from atleast one spoked web member 124, with a rotor pole 122 mounted at thedistal end of each spoke of the spoked web member 124. Thus, the rotor118 includes N=6 rotor poles 122 corresponding to the N=6 stator poles112.

Each stator pole 112 comprises a primary stator pole PSP and an axiallyaligned auxiliary stator pole ASP (neither shown explicitly here, seeFIG. 3). Illustration of the windings for the stator poles 112 isomitted in FIG. 2 because the primary stator pole PSP and axiallyaligned auxiliary stator pole ASP are separately wound and this cannotbe adequately illustrated with the view of FIG. 2. More detail on theseparate windings provided for the stator poles 112 (i.e., the primarystator pole PSP and auxiliary stator pole ASP) is provided in FIGS. 3,6A and 6B.

Reference is now made to FIG. 3 which illustrates a cross-sectional viewtaken along lines 3-3 of FIG. 2. The shaft 120 rotates about an axis126. Although not shown in FIG. 3, the two opposed ends of the shaft 120are supported for such rotation by an end housing and bearing system ina manner well known to those skilled in the art (see, FIGS. 10, 11A and11B). The shaft 120 may be made of any suitable material, including 1045steel. The spoked web member 124 is mounted to the shaft and retained tobe rotated with the shaft 120 without slipping. An appropriate fasteningmechanism and keying system, as is well known to those skilled in theart, may be used to secure the spoked web member 124 to the shaft 120.The spoked web member 124 may be made of any suitable material,including mild or low hysteresis steel, aluminum or composite materials.Importantly, and unlike prior art implementations, the spoked web member124 need not be made of a material which supports magnetic flux.Openings 128 (see, FIG. 2) are provided in each spoke of the spoked webmember 124 to reduce the overall weight of the rotor 118 and position agreater proportion of the rotor's overall weight towards the perimeterof the rotor. One rotor pole 122 is mounted to the distal end of eachspoke of the spoked web member 124. Each rotor pole 122 extends in anaxial direction parallel to the shaft 120. FIG. 3 specificallyillustrates the use of two spoked web members 124 to support oppositeends of each one of the N=6 rotor poles 122, but it will be understoodthat just a single spoked web member 124 could instead be used. Eachrotor pole 122 may be made of any suitable material, including mild orlow hysteresis steel, provided that the material supports a magneticflux path in and along the length of the rotor pole 122 extending in theaxial direction. Solid bar stock is preferred for the rotor pole 122,but laminated materials stacked parallel to the axial direction couldalso be used to form a suitable rotor pole.

The stator 110 is formed of a lamination of ring members, wherein thelaminated materials are stacked perpendicular to the axial direction.The ring members include a spacer ring member 140 (see, FIG. 4) and astator pole ring member 142 (FIG. 5). The ring members 140 and 142 maybe made of any suitable material, including low hysteresis steel orother conventional laminate steel. The lamination of ring members toform a stator 110 with stator poles 112 is well known to those skilledin the art. Openings 125 are provided about the perimeter of the ringmembers 140 and 142 to assist in alignment and lamination of the statorring members to form the stator 110. These openings further support thepassage of a fastening means, such as a long bolt, when assembling thering members together to form a stator.

The stator 110 is different from prior art laminated statorconfigurations in that each included stator pole 112 comprises a primarystator pole PSP and an axially aligned auxiliary stator pole ASP. Theprimary stator poles PSP are formed from a first lamination 144 of aplurality of stator pole ring members 142 (FIG. 5). The auxiliary statorpoles ASP are formed from a second lamination 146 of a plurality ofstator pole ring members 142 (FIG. 5). It will be noted that the firstlamination 144 includes more stator pole ring members 142 (FIG. 5) inthe stack than the second lamination 146. Thus, the primary stator polesPSP are larger (i.e., axially longer) than the axially aligned auxiliarystator poles ASP. The first lamination 144 forming the primary statorpoles PSP is separated from the second lamination 146 forming theaxially aligned auxiliary stator poles ASP by a third lamination 148 ofa plurality of spacer ring members 140 (see, FIG. 4). The stator 110 iscompleted by a fourth lamination 150 of a plurality of spacer ringmembers 140 (see, FIG. 4) mounted to the first lamination 144 (thisfourth lamination 150 separating the first lamination 144 for theprimary stator poles PSP away from a first end of the machine), and afifth lamination 152 of a plurality of spacer ring members 140 (see,FIG. 4) mounted to the second lamination 146 (this fifth lamination 152separating the second lamination 146 for the auxiliary stator poles ASPaway from a second end of the machine). Laminated construction withrespect to the primary stator poles PSP (first lamination 144) and withrespect to the axially aligned auxiliary stator poles ASP (secondlamination 146) is preferred so that the supported magnetic flux pathsin the stator are restrained in the radial and circumferentialdirections.

As mentioned above, each rotor pole 122 extends in an axial directionparallel to the shaft 120. The rotor poles 122 have an axial lengthsubstantially equal to a combined axial length of the PSP firstlamination 144, ASP second lamination 146 and spacing third lamination148. In other words, each rotor pole has an axial length sufficient tosubstantially and simultaneously cover the primary stator pole PSP andauxiliary stator pole ASP.

The primary stator pole PSP and the axially aligned auxiliary statorpole ASP of each included stator pole 112 are separately wound. Detailsof this separate winding are provided below with respect to FIGS. 6A,6B, 7A and 7B.

Reference is now made to FIG. 6A which shows the first lamination 144for the primary stator poles PSP (made of a plurality of stacked statorpole ring members 142). Each primary stator pole PSP is wound with awinding 160. The windings 160 for the six primary stator poles PSP areelectrically connected in parallel (see, also, FIG. 7A). The windingdirection for each winding 160 is indicated using the “×” and “●”nomenclature (as described above). With the illustrated windingorientation, it will be noted that the magnetic orientation of theprimary stator poles PSP when actuated alternates /S-N-S-N-S-N/ aroundthe circumference of the stator 110. The windings 160 for the primarystator poles PSP are also shown in FIG. 3.

Reference is now made to FIG. 6B which shows the second lamination 146for the auxiliary stator poles ASP (made of a plurality of stackedstator pole ring members 142). Each auxiliary stator pole ASP is woundwith a winding 162. The windings 162 for pairs 180 of the six auxiliarystator poles ASP are electrically connected in series (see connection164) and the resulting three pairs 180 of windings 162 are connected inparallel (see, also, FIG. 7B). The winding direction is again indicatedusing the “×” and “●” nomenclature. With the illustrated windingorientation, it will be noted that the magnetic orientation of theauxiliary stator poles ASP when actuated alternates /N-S-N-S-N-S/ aroundthe circumference of the stator 110. Importantly, this magneticorientation is opposite (or reversed from) the /S-N-S-N-S-N/ of theprimary stator poles PSP (FIG. 6A) such that the primary stator pole PSPand its axially aligned auxiliary stator pole ASP for a given statorpole 112 have opposite magnetic orientations (for example, for onestator pole 112, the included primary stator pole PSP will have an Norientation and the axially aligned auxiliary stator pole ASP will havean S orientation, or vice-versa). The windings 162 for the auxiliarystator poles ASP are also shown in FIG. 3.

Reference is now made to FIG. 7A which illustrates the parallel circuitconnection of the windings 160 for the primary stator poles PSP of FIG.6A. The windings 160 are connected in parallel between a first node 170and a second node 172. When the primary stator poles PSP are actuated,current flow 182 through the windings 160 is in a direction from thefirst node 170 towards the second node 172. Each winding 160 has a firstend 174 and a second end 176. It will be noted that the end (174 or 176)which is connected to the first node 170 alternates with respect toadjacent ones of the primary stator poles PSP. Likewise, the end (174 or176) which is connected to the second node 172 alternates with respectto adjacent ones of the primary stator poles PSP. The alternatingconnection of the first end 174 and second end 176 to the first node 170and second node 172 produces alternating winding orientations for theprimary stator poles PSP (as is shown in FIG. 6A) so that the magneticorientation of the primary stator poles PSP when actuated alternates/S-N-S-N-S-N/ around the circumference of the stator 110.

Reference is now made to FIG. 7B which illustrates the series/parallelcircuit connection of the windings 162 for the auxiliary stator polesASP of FIG. 6B. Pairs 180 of the windings 162 are connected in series byconnection 164. The pairs 180 are then connected in parallel between thefirst node 170 and the second node 172. Each series connection of twowindings 162 includes a pair of series connected zener diodes 178oriented with their anodes pointing towards the second node 172 andtheir cathodes pointing towards the first node 170. This configurationof the zener diodes 178 precludes current flow through the seriesconnected windings 162 in a direction from the first node 170 towardsthe second node 172, but permits current flow in the opposite direction(the reason for this is discussed in detail below, as is the reason forconnecting pairs 180 of windings 162 in series). When the auxiliarystator poles ASP are actuated, current flow 184 through the windings 162is in a direction from the second node 172 towards the first node 170.Each winding 162 has a first end 174 and a second end 176. It will benoted that the series connection 164 of the second ends 176 of the pairsof windings 162 produces alternating winding orientations for theauxiliary stator poles ASP (as is shown in FIG. 6B) so that the magneticorientation of the auxiliary stator poles ASP when actuated alternates/N-S-N-S-N-S/ around the circumference of the stator 110 (this being theopposite of the /S-N-S-N-S-N/ configuration for the primary stator polesPSP).

Reference is now made to FIG. 8 which illustrates a schematic diagram ofa drive circuit 200 for the switched reluctance machine. A power supply202 has a more positive node 204 and a more negative node 206. The morepositive node 204 could be a positive supply node, and the more negativenode 206 could be a ground node. Conversely, the more positive node 204could be a ground node, and the more negative node 206 could be anegative supply node. The more positive node 204 is coupled to the firstnode 170. Coupled between the first node 170 and the second node 172 isa capacitor 210 (optional but recommended to retard a high frequencyrunaway condition). Also coupled between the first node 170 and secondnode 172 is the primary stator poles PSP winding circuit shown in FIG.7A and the auxiliary stator poles ASP winding circuit shown in FIG. 7B.FIG. 8 does not illustrate all of the windings 160 and 162 as shown inFIGS. 7A and 7B. Rather, only four of the windings 160 and four of thewindings 162 are shown to simplify the drawing.

FIG. 8 further illustrates the shared electrical and magnetic connectionrelationship of the primary stator poles PSP winding circuit (FIG. 7A)and the auxiliary stator poles ASP winding circuit (FIG. 7B) relative tothe first node 170 and second node 172. The format of the windingconnections and orientations in FIG. 8 is different from that shown inFIGS. 7A and 7B in order to simplify the circuit drawing and assist inmaking the operation of the circuit 200 more understandable. Withrespect to the physical implementation in forming the primary statorpoles PSP and the auxiliary stator poles ASP, the windings 160 and 162are drawn with different orientations (left and right) to indicate theuse of alternate winding directions. Each winding 160 and 162 is furtherprovided with a labeled arrow (N→ or S→). The arrow direction isconsistent with the direction of current flow when the respective statorpoles are actuated. The label (either “N” or “S”) indicates theorientation of the magnetic field produced in response to that directionof current flow (noting again that the magnetic orientation alternates/S-N-S-N-S-N/ around the circumference of the stator 110 for the primarystator poles PSP, and alternates /N-S-N-S-N-S/ around the circumferenceof the stator 110 for the auxiliary stator poles ASP). Still furtherwith respect to the physical implementation, FIG. 8 includes a labeleddashed bi-directional arrow (N← - - →S or S← - - →N) 210 indicating theaxial alignment between one primary stator pole PSP (with winding 160)and its axially aligned auxiliary stator pole ASP (with winding 162), aswell as indicating the magnetic coupling between one primary stator polePSP and its axially aligned auxiliary stator pole ASP. As will bediscussed below, that magnetic coupling is provided through the axiallyextending rotor pole 122. Thus, the bi-directional arrow 210 may beunderstood to represent a rotor pole 122. The label (either “N” or “S”)on the end of the bi-directional arrow 210 indicates the orientation ofthe magnetic field in the rotor pole 122 when the primary stator polePSP and auxiliary stator pole ASP are actuated.

An axially aligned 210 primary stator pole PSP and auxiliary stator poleASP define one stator pole 112 as is shown in FIGS. 2 and 3. It will benoted that when actuated, the primary stator pole PSP has one magneticfield orientation (for example, N) while its axially aligned auxiliarystator pole ASP has the opposite magnetic field orientation (forexample, S). The two ends of the rotor pole 220 (schematicallyrepresented by the bi-directional arrow 210) will have opposite magneticfield orientations (S and N, respectively, for this example) and thuswill be attracted to the stator pole 112. It is this attraction whichproduces torque causing rotation of the rotor.

The second node 172 is coupled to the drain D of an n-channel powerswitching MOSFET 212. An optional snubber diode 208 may be insertedbetween the second node 172 and the drain D of the n-channel powerswitching MOSFET 212. A speed control circuit 214 is coupled between thesource S of the MOSFET 212 and the more negative node 206 of the powersupply 202. The speed control circuit 214 may comprise, for example, anAlltrax speed controller. The gate G of the MOSFET 212 is coupled to theoutput of a drive control circuit 216. The drive control circuit 216generates a gate drive signal to control switching on/off of the MOSFET212. Changes in state of the gate drive signal are produced in responseto information relating to the angular position of the rotor. Thisobtained angular position of the rotor is detected by an angularposition sensor 218. The sensor 218 in a preferred implementationcomprises an optical sensor coupled to the shaft of the rotor. Suchoptical sensors are well known to those skilled in the art (see, also,FIG. 13).

The general functional operation of the MOSFET 212, drive controlcircuit 216 and angular position sensor 218 will now be described. Theangular position sensor 218 detects the angular position of the rotor,and more specifically detects the position of the rotor poles relativeto the stator poles. Responsive to detection by the angular positionsensor 218 of a desired relative position relationship between thosepoles (such as the position shown in FIG. 9A), the drive control circuit216 generates the gate drive signal with a state to turn on the MOSFET212. Assuming that the speed control circuit 214 is also activated,current will flow from the more positive node 204 of the power supply202 towards the more negative node 206. This current flows through thewindings 160 and simultaneously activates the primary stator poles PSP.In this mode, the zener diodes 178 prevent current from flowing throughthe windings 162 of the auxiliary stator poles ASP in a direction fromthe first node 170 to the second node 172 (i.e., these stator poles arenot actuated).

At this point, the motor is operating in a manner generally similar tothat shown and described above with respect to FIGS. 1A and 1B. Therotor poles 122 are attracted to the energized stator poles 112, andmore particularly to the primary stator poles PSP, producing a torque onthe shaft 120 as the rotor poles 122 move towards the energized statorpoles 112 in an effort to minimize the reluctance. However, unlike theimplementation of FIGS. 1A and 1B, the magnetic flux paths do notprimarily run through the spoked web member 124, but rather run alongthe length of the rotor poles 122 and through the (un-actuated)auxiliary stator poles ASP. This flux configuration is described indetail below and illustrated in connection with FIGS. 9B, 9C and 9Ewhere the auxiliary stator poles ASP are actuated.

When the angular position sensor 218 detects that the rotor poles 122have moved close to the position of minimized reluctance, for examplewhere the rotor pole 122 is nearly, but not completely, aligned with thestator pole 112 (such as the position shown in FIG. 9B), the drivecontrol circuit 216 turns off the MOSFET 212. This isolates the secondnode 172 from the more negative node 206 of the power supply 202. Alarge high voltage inductive pulse is then generated at the second node172. In prior art implementations, this large high voltage inductivepulse is typically dissipated and the stored magnetic energy in thestator windings is wasted. In the motor embodiment described herein,however, the stored magnetic energy is put to more productive use.

The large high voltage inductive pulse at second node 172 has a voltagemagnitude that is sufficient to forward bias the zener diodes 178 (thusactuating the auxiliary stator poles ASP). The generated inductive pulseis accordingly dumped through the pairs of series connected windings 162for the auxiliary stator poles ASP. Because of the size of the inductivepulse, a large impedance must be present in the dumping circuit path.This large impedance is provided by connecting two of the windings 162for the auxiliary stator poles ASP in series. It will, however, beunderstood that the windings 162 for the auxiliary stator poles ASPcould instead be connected in parallel (similar to that of the windings160 for the primary stator poles ASP) provided that a single winding 162presented a sufficiently high impedance value in relation to the highvoltage inductive pulse.

The magnetic flux paths with respect to the actuated primary statorpoles PSP, actuated auxiliary stator poles ASP and the rotor poles 122are shown in FIG. 9B (for the primary stator poles PSP), FIG. 9C (forthe auxiliary stator poles ASP) and FIG. 9E for the stator and rotorpoles together. These paths flow from a first primary stator pole andcross the air gap to a first end of a first rotor pole (path segment500), flow along the length of the first rotor pole to a second end ofthe first rotor pole (path segment 502), cross the air gap to a firstauxiliary stator pole (that is axially aligned with the first primarystator pole) (path segment 504), flow from the first auxiliary statorpole in the stator laminations to a second auxiliary stator poleadjacent thereto (path segment 506), cross the air gap from the secondauxiliary stator pole to a first end of a second rotor pole (pathsegment 508), flow along the length of the second rotor pole to a secondend of the second rotor pole (path segment 510), and cross the air gapfrom the second rotor pole to a second primary stator pole (that isadjacent to the first primary stator pole) (path segment 512), and flowfrom the second primary stator pole in the stator laminations to thefirst primary stator pole adjacent thereto (path segment 514). FIGS. 9Band 9C additionally show the portion of the magnetic flux paths whichpass axially along the length of the rotor pole 122 in a separatebreakout, while these paths are shown in context with the statormagnetic flux paths in FIG. 9E.

The rotor poles 122 continue to be attracted to the energized statorpoles 112, at this point actively to both the primary stator poles PSPand the auxiliary stator poles ASP, producing a continued torque on theshaft 120 as the rotor poles 122 continue to move towards the energizedstator poles 112 in an effort to minimize the reluctance.

At this point, because the MOSFET 212 has been turned off, and becausethe inductive pulse has been completely dumped and put to work throughthe windings 162 of the auxiliary stator poles ASP, the stator poles 112are now de-energized. Angular momentum is preserved and the rotorcontinues to rotate such that the rotor pole 122 passes past thede-energized stator pole 112. After a delay period which allows therotor pole 122 to move sufficiently away from the stator pole 112 (i.e.,closer to the next stator pole as shown in FIG. 9A), the angularposition sensor 218 again senses that the rotor is in the desiredrelative position relationship, the drive control circuit 216 turns onthe MOSFET 212, and the process repeats.

Speed of rotor rotation can be controlled by changing the currentsupplied to the windings 160 of the primary stator poles PSP. This isaccomplished by operation of the speed control circuit 214 to adjust thevoltage drop from the source S of the MOSFET 212 to the more negativenode 206 of the power supply 202.

Reference is now made to FIG. 10 which illustrates a partialcross-section and side view of the switched reluctance machine 400 asdescribed above. End housing members 182 and 184 are provided atopposite ends of the machine. A bearing system 186 is installed on eachhousing member to support rotation of the shaft 120. One end of theshaft 120 is coupled to an angular position sensor 190. Such sensors arewell known to those skilled in the art. In a preferred implementation,the sensor 190 is implemented as an optical light gap sensor. A slottedwheel is mounted to the shaft, with the slots having a known positionalrelationship relative to the positions of the rotor poles and statorpoles. Light is projected onto the wheel to pass through the slots. Alight sensor detects the light passing through the slots in the wheel,and the detected light provides information concerning position of therotor poles. See, also, FIG. 13.

The machine 400 as shown in FIG. 10, when configured as a motor, is notself-starting because the rotor could stop rotating at a position wherethe rotor poles were aligned with the stator poles (the minimizedreluctance position). To address this issue, the motor of FIG. 10 couldfurther include a parking magnet which attracts the rotor poles to aposition offset from the stator poles and from which starting ispossible. Alternatively, the rotor poles could be shaped with aconfiguration that permits self-starting from any rotor positionincluding when aligned with the stator poles. Parking magnet andself-starting rotor pole shape solutions are well known to those skilledin the art.

In a further embodiment, multiple switched reluctance machines 400 (onesuch machine 400 as is shown in FIG. 10) can be stacked on a commonshaft 120. By angularly offsetting the multiple machines from eachother, the stacked machine presents a motor configuration that isself-starting because the rotor poles of at least one of the machines400 will be sufficiently offset from the stator poles to allow formagnetic attraction and torque generation. For example, the angularoffset could be introduced by angularly offsetting the stator poles andkeeping the rotor poles in alignment. This configuration is shown inFIGS. 11A and 11C. In FIG. 11A it will be noted that dotted boxes areused to indicate the location of the angularly offset stator poles 112,while FIG. 11C illustrates that angular offset. Alternatively, theangular offset could be introduced by angularly offsetting the rotorpoles and keeping the stator poles in alignment. This configuration isshown in FIG. 11B. An angular offset of 360/(M*N) degrees between eachof the included machines 400 is acceptable (when M is the number ofmachines 400 in the stack). In the implementation of FIGS. 11A and 11B,the angular offset may, for example, comprise 10-25 degrees. FIGS. 11Aand 11B specifically illustrate a preferred angular offset betweenmachines 400 of 20 degrees (360/(3*6)).

End housing members 182 and 184 are provided at opposite ends of themachine. A bearing system 186 is installed on each housing member tosupport rotation of the shaft 120. One end of the shaft 120 is coupledto a set of angular position sensors 192. Such sensors are well known tothose skilled in the art. In a preferred implementation, the sensors 192are each implemented as an optical light gap sensor. A slotted wheel ismounted to the shaft, with the slots having a known positionalrelationship relative to the position of the rotor poles relative to thestator poles. Light is projected onto the wheel to pass through theslots. A light sensor associated with each machine 400 detects the lightpassing through the slots in the wheel, and the detected light providesinformation concerning position of the rotor poles. See, also, FIG. 13.

Reference is now made to FIG. 12 which illustrates a schematic diagramof a drive circuit for the switched reluctance machine of FIGS. 11A and11B. Because multiple switched reluctance machines 400 are present,multiple drive circuits are required. Each drive circuit is of the typeshown in FIG. 8 and previously described. The circuit of FIG. 12,however, shares speed control 214 across the three machines, and theangular position sensors 218 provide position information relative toeach of the machines 400.

Reference is now made to FIG. 13 which illustrates a schematic diagramof an angular position sensor 218 and drive control circuit 216 used inFIGS. 8 and 12. One circuit as shown in FIG. 13 is needed for eachmachine included in the stack of FIGS. 11A and 11B. The angular positionsensor utilizes a slotted wheel 500 is mounted to the shaft 120 of theswitched reluctance machine. A fork-type optical sensor 502 ispositioned to straddle the slotted wheel 500. An example of such asensor is a Pepperl & Fuchs GL10-RT/32/40A/98A sensor. The sensor 502 ispowered from a first voltage supply 504. A capacitor C1 is connectedacross the supply terminals of the first voltage supply 504. The outputof the sensor 502 is applied to a voltage divider formed by resistors R1and R2 connected in series. An output of the voltage divider is appliedto the input of an opto-isolated FET driver circuit 506. An example ofsuch a driver circuit 506 is an Avago ACNW3190 integrated circuit. Thedriver circuit 506 is powered from a second voltage supply 508. Acapacitor C2 is connected across the Vcc and Vee supply terminals of thesecond voltage supply 508. The supply 508 further provides a groundterminal. The output of the opto-isolated FET driver circuit 506 isapplied through a resistor network R3 and R4 to the common gateterminals of a push-pull FET driver circuit 510. The circuit 510includes an n-channel FET M1 connected in series with a p-channel FET M2between the Vcc and Vee supply terminals of the second voltage supply508. The output of the push-pull FET driver circuit 510 (taken at theconnected source terminals of FETs M1 and M2) is applied throughresistor R5 to gate terminal (G) of the switching transistor 212 (FIGS.8 and 12).

In operation, the fork-type optical sensor 502 detects the presence of aslot in the rotating slotted wheel 500. That detection is supplied tothe input of the opto-isolated FET driver circuit 506 providing signalisolation and generating at its output a corresponding detect signal.The detect signal turns on transistor M1 of the push-pull FET drivercircuit 510 (transistor M2 is off) and a gate drive signal is generatedwhich turns on the switching transistor 212 (FIGS. 8 and 12). When theslot in the rotating slotted wheel 500 is no longer detected by thefork-type optical sensor 502, this detection is signal isolated throughthe opto-isolated FET driver circuit 506 which generates a correspondingno-detect signal. Responsive to the no-detect signal, transistor M2 ofthe push-pull FET driver circuit 510 is turned on (transistor M1 is off)and a gate drive signal is generated which turns off the switchingtransistor 212 (FIGS. 8 and 12).

Reference is once again made to FIGS. 8 and 12. The switching transistor212 must be a high voltage and high current device. Indeed, for thelarge currents present when the switching transistor 212 is turned on,it may be preferable for the switching transistor 212 to be implementedas a plurality of parallel connected transistor devices, where currentis divided between the included devices. Accordingly, it will berecognized that switching transistor 212 as illustrated represents oneor more actual transistor devices. Nonetheless, the switching transistor212, in handling high current and high voltage, will generate asignificant amount of heat. It is critical that this generated heat bedissipated.

Referring now to FIG. 14, there is illustrated a heat dissipationconfiguration for the switching transistor 212. A thermally conductivebox structure 600 with an open (and perhaps baffled) interior isprovided. Attached to one side 602 of the box structure 600 is theswitching transistor 212. Of course, if multiple devices are requiredfor implementing the switching transistor 212, there will be multipledevices attached to the side 602 of the box structure 600. Theillustration of single device in FIG. 14 is exemplary only. The boxstructure 600 includes two ports 604 and 606. The port 604 is coupled608 to a first port 610 of a radiator 612. The radiator 612 may be ofany known design including, for example, radiators of the typeconventionally used in automobiles. The port 606 is coupled 614 to oneside of a fluid pump 616. The other side of the fluid pump 616 iscoupled 618 to a second port 620 of the radiator 612. The radiator 612may include a fan 622 for circulating air across the fins of theradiator. The box structure 600, coupling lines, and radiator 612 arefilled with an appropriate coolant. This coolant may be any suitablecoolant fluid. In a preferred embodiment the coolant fluid ispolyethylene glycol.

Reference is now made to FIG. 15 which illustrates use of the switchedreluctance machine SRM as described herein as the power plant for anelectric vehicle application. The switched reluctance machine SRM asdescribed herein may be used in place of an internal combustion enginein an automobile. The shaft 120 of the switched reluctance machine SRMis coupled, for example, to a conventional automobile transmission whichdrives one or more axles of the vehicle. Although illustrated in FIG. 15in a rear-wheel drive configuration, it will be understood that theswitched reluctance machine SRM could be used in other driverconfigurations including front wheel drive and all-wheel drive. Powerfor switched reluctance machine SRM operation is supplied from a batterybank. The battery bank may utilize any type of batteries. Lead acidbatteries comprise one option for use in the battery bank. Anotheroption is to use lithium-based batteries. Nicad batteries may also beused. Advantageously, the implementation may utilize the existingradiator for the vehicle (see, FIG. 14). Thus, the switched reluctancemachine SRM could be configured with shaft 120 mating to a conventionalautomobile transmission and the switched reluctance machine SRM simplybeing swapped in place of the internal combustion engine. This wouldallow a legacy vehicle designed for an internal combustion engine powerplant to be retrofitted into an electric vehicle application using theswitched reluctance machine SRM power plant.

FIG. 16 illustrates an alternative implementation. In thisimplementation, a separate switched reluctance machine SRM is providedfor each wheel of the vehicle (either 2 wheel drive or 4 wheel drive).The driver circuitry would be connected to actuate each switchedreluctance machine SRM (where each SRM may include one or more stackswith M>=1). The switched reluctance machine SRM may, for example,directly drive its associated wheel. Alternatively, a gearing and/ortransmission system may be implemented between the switched reluctancemachine SRM and its associated wheel. In this implementation, it mayfurther be advantageous to implement the switched reluctance machine SRMwith the stator inside the rotor. In other words, the stator would belocated in the center of the machine and the rotor would be positionedaround and rotate about the stator. This implementation would thenpermit the rotor to be configured as a structural component of the wheelof the vehicle.

The preferred switched reluctance machine SRM for use in an automobileapplication like that of FIG. 15 would comprise one of the stackedimplementation shown in FIGS. 11A and 11B. A switched reluctance machineSRM of this type configured as a motor has been built and tested for usein an electric vehicle application. The motor has M=3 machines 4000,each machine having N=6 stator poles, N*=6 rotor poles, a statordiameter of 6-18 inches, a rotor diameter of 2-12 inches, a rotor polelength of 2-6 inches, a PSP length of 0.5-3 inches, an ASP length of0.25-2 inches, and a pole width of 0.75-3 inches. The motor, whenconfigured with a stator diameter of 14-18 inches, a rotor diameter of9-12 inches, a rotor pole length of 4 inches, a PSP length of 2 inches,an ASP length of 1.5 inches, and a pole width of 2 inches and testedwith a battery bank of sixteen 6V lead acid batteries (a total of about100 volts), produced a maximum speed of 2200 rpm, a maximum torque of 60ft.-lbs. and a maximum power consumption of 18 K-watts. With thisoutput, the switched reluctance machine SRM is an acceptable power plantreplacement for many four and six cylinder internal combustion engines.

Other applications may utilize single stack or double stack switchedreluctance machine SRM configurations (a single stack configurationbeing illustrated in FIG. 10). A switched reluctance machine SRM with alarger stack (i.e., M>3) may also be used for heavier duty (largertorque and power) applications provided sufficient space is availablefor the installation.

Although the embodiments illustrated and described herein relate to areluctance machine where the rotor is inside the stator, it will beunderstood that the disclosed reluctance machine could alternatively beconfigured with the stator inside the rotor.

Although preferred embodiments of the method and apparatus of thepresent invention have been illustrated in the accompanying Drawings anddescribed in the foregoing Detailed Description, it will be understoodthat the invention is not limited to the embodiments disclosed, but iscapable of numerous rearrangements, modifications and substitutionswithout departing from the spirit of the invention as set forth anddefined by the following claims.

1. An electric vehicle, comprising: at least one drive wheel; and a power plant adapted to supply torque for causing rotation of the at least one drive wheel, wherein the power plant comprises at least one switched reluctance motor, the switched reluctance motor comprising: a stator having a plurality of stator poles; a rotor having a plurality of rotor poles and configured to rotate a shaft supplying the torque about an axis of rotation; wherein each of the stator poles comprises: a primary stator pole; and an auxiliary stator pole, wherein the auxiliary stator pole is axially aligned with the primary stator pole in the direction of the axis of rotation; wherein each rotor pole has a length extending in the direction of the axis of rotation sufficient to at least partially cover both the primary stator pole and axially aligned auxiliary stator pole; and wherein each rotor pole supports an axial magnetic flux path extending between the primary stator pole and the axially aligned auxiliary stator pole.
 2. The vehicle of claim 1 further comprising a transmission coupled between the switched reluctance motor power plant and the at least one drive wheel.
 3. The vehicle of claim 1 wherein the power plant comprises a first power plant supplying first torque for actuating a first one of the at least one drive wheel and a second power plant supplying second torque for actuating a second one of the at least one drive wheel, each one of the first and second power plants comprising said switched reluctance motor.
 4. The vehicle of claim 1 wherein each of the primary stator poles has a first winding, the first windings for all primary stator poles in said switched reluctance motor being electrically connected in parallel but with adjacently opposite winding directions so that the plurality of primary stator poles exhibit alternating magnetic orientations about a perimeter of the stator; and wherein the auxiliary stator pole and primary stator pole are oriented at a same angular position with respect to each other.
 5. The vehicle of claim 4 wherein each of the auxiliary stator poles has a second winding, the second windings for the auxiliary stator poles being electrically connected with adjacently opposite winding directions so that the plurality of auxiliary stator poles exhibit alternating magnetic orientations about the perimeter of the stator and wherein the alternating magnetic orientations for the plurality of primary stator poles and the alternating magnetic orientations for the plurality of auxiliary stator poles are arranged oppositely such that in each stator pole the primary stator pole has one magnetic orientation and the axially aligned auxiliary stator pole has an opposite magnetic orientation.
 6. The vehicle of claim 5 wherein the electrical connection of the second windings for the auxiliary stator poles connects pairs of the second windings for the auxiliary stator poles in series, with the pairs of windings being electrically connected in parallel.
 7. The vehicle of claim 1 further comprising a drive circuit configured to simultaneously actuate the stator poles and wherein the drive circuit comprises a switching transistor having a control terminal and a first conduction terminal, and wherein each of the primary stator poles has a first winding, the first windings for all primary stator poles in said switched reluctance motor being electrically connected in parallel between a more positive reference node and the first conduction terminal of the switching transistor.
 8. The vehicle of claim 7 wherein the first windings for the primary stator poles are electrically connected in parallel but with adjacently opposite winding directions so that the plurality of primary stator poles exhibit alternating magnetic orientations about a perimeter of the stator and wherein second windings for the auxiliary stator poles are electrically connected with adjacently opposite winding directions so that the plurality of auxiliary stator poles exhibit alternating magnetic orientations about the perimeter of the stator.
 9. The vehicle of claim 7 wherein each of the auxiliary stator poles has a second winding, the second windings for the auxiliary stator poles being electrically connected between the more positive reference node and the first conduction terminal of the switching transistor, and wherein the electrical connection of the second windings includes a series connected diode circuit wherein an anode of the diode circuit is connected with an orientation towards the first conduction terminal of the switching transistor and a cathode the diode circuit is connected with an orientation towards the more positive reference node.
 10. The vehicle of claim 9 wherein the electrical connection of the second windings for the auxiliary stator poles connects pairs of the second windings for the auxiliary stator poles in series, with the pairs of windings being electrically connected in parallel and wherein the alternating magnetic orientations for the plurality of primary stator poles and the alternating magnetic orientations for the plurality of auxiliary stator poles are arranged oppositely such that in each stator pole the primary stator pole has one magnetic orientation and the axially aligned auxiliary stator pole has an opposite magnetic orientation.
 11. The vehicle of claim 7 further comprising a battery bank for supplying electrical power to the power plant, the bank having a first terminal coupled to the more positive node and a second terminal coupled to a second conduction terminal of the switching transistor and a speed control circuit coupled between the second terminal of the battery bank and the second conduction terminal of the switching transistor.
 12. The vehicle of claim 7 further comprising a snubber diode coupled in series with the first conduction terminal of the switching transistor.
 13. The vehicle of claim 1, wherein said at least one switched reluctance motor for the power plant comprises M switched reluctance motors stacked on a common axis of rotation, wherein M>1.
 14. The vehicle of claim 13 wherein the power plant comprises a first set of M switched reluctance motors supplying first torque for actuating a first one of the at least one drive wheel and a second set of M switched reluctance motors supplying second torque for actuating a second one of the at least one drive wheel.
 15. An electric vehicle comprising: at least one drive wheel; and a power plant adapted to supply torque for causing rotation of the at least one drive wheel, wherein the power plant comprises at least one switched reluctance motor, the switched reluctance motor comprising: a stator having a plurality of stator poles; a rotor having a plurality of rotor poles and configured to rotate a shaft supplying the torque about an axis of rotation; wherein each of the stator poles comprises: a primary stator pole; and an auxiliary stator pole, wherein the auxiliary stator pole is axially aligned with the primary stator pole in the direction of the axis of rotation; wherein each rotor pole has a length extending in the direction of the axis of rotation sufficient to at least partially cover both the primary stator pole and axially aligned auxiliary stator pole; and wherein the plurality of stator poles consists of N stator poles and wherein the plurality of rotor poles consists of N rotor poles, wherein N is an even integer, and further comprising: a drive circuit configured to simultaneously actuate the N stator poles; wherein simultaneous actuation of the N stator poles comprises: a simultaneous actuation of the primary stator poles for the N stator poles; and a simultaneous actuation of the auxiliary stator poles for the N stator poles.
 16. The vehicle of claim 15 wherein the primary stator poles for the N stator poles are simultaneously actuated in a first phase responsive to actuation of a switching transistor coupled in series with windings for both the primary stator poles and the auxiliary stator poles and wherein the auxiliary stator poles for the N stator poles are simultaneously actuated in a second phase responsive to de-actuation of the switching transistor coupled in series with windings for both the primary stator poles and the auxiliary stator poles.
 17. The vehicle of claim 16 wherein the windings for the primary stator poles are coupled in parallel with the windings for the auxiliary stator poles.
 18. The vehicle of claim 17 further comprising diode circuitry coupled in series with the windings for the auxiliary stator poles to block current flow in the windings for the auxiliary stator poles during the first phase and permit current flow in the windings for the auxiliary stator poles during the second phase.
 19. An electric vehicle, comprising: at least one drive wheel; and a power plant adapted to supply torque for causing rotation of the at least one drive wheel, wherein the power plant comprises at least one switched reluctance motor, the switched reluctance motor comprising: a stator having a plurality of stator poles; a rotor having a plurality of rotor poles and configured to rotate a shaft supplying the torque about an axis of rotation; wherein each of the stator poles comprises: a primary stator pole; and an auxiliary stator pole, wherein the auxiliary stator pole and primary stator pole are oriented at a same angular position with respect to each other; wherein each rotor pole has a length extending in the direction of the axis of rotation sufficient to at least partially cover both the primary stator pole and the auxiliary stator pole at the same angular position.
 20. The vehicle of claim 19, wherein each rotor pole supports an axial magnetic flux path extending between the primary stator pole and the auxiliary stator pole oriented at the same angular position as the primary stator pole. 